Light-emitting device

ABSTRACT

A structure of an EL display device which has an increased display area is provided. Further, a structure of an EL display device which has a high definition display is provided. An auxiliary electrode is formed over a first partition and side surfaces of the auxiliary electrode are covered with a second partition. A top surface of the auxiliary electrode is in contact with the conductive film which is one electrode of a light-emitting element and has a light-transmitting property, which enables a large-area display. Further, even the distance between the adjacent light-emitting elements is shortened, the auxiliary electrode can be provided between the adjacent light-emitting elements, which enables a high definition display.

This application is a continuation of copending U.S. application Ser.No. 13/887,831, filed on May 6, 2013 which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device, a method formanufacturing the display device, and an electronic appliance includingthe display device.

In this specification, a semiconductor device generally means a devicewhich can function by utilizing semiconductor characteristics, and anelectrooptic device, a semiconductor circuit, and an electronicappliance are all semiconductor devices.

2. Description of the Related Art

A transistor formed over a glass substrate or the like includesamorphous silicon, polycrystalline silicon, or the like, as typicallyseen in a liquid crystal display device or an EL display device.Although a transistor using amorphous silicon has low field effectmobility, it can be formed over a larger glass substrate. On the otherhand, although a transistor using polycrystalline silicon has high fieldeffect mobility, it is not suitable for being formed over a larger glasssubstrate.

In contrast to a transistor using silicon, attention has been focused ona technique of manufacturing a transistor using an oxide semiconductorand applying such a transistor to an electronic appliance or an opticaldevice. For example, a technique of manufacturing a transistor usingzinc oxide or In—Ga—Zn—O-based oxide as an oxide semiconductor, andusing such a transistor for a switching element of a pixel in a displaydevice and the like is disclosed in Patent Document 1 and PatentDocument 2.

Further, display devices with large display areas have increasinglybecome popular. Televisions with display screens having a diagonal of 40inches to 50 inches are becoming common as home televisions and areexpected to become more popular in the future. As described above, thefield effect mobility of the transistor using an oxide semiconductor isten or more times as high as that of the transistor using amorphoussilicon; therefore, the performance of the transistor using an oxidesemiconductor is high enough to allow the use of the transistor as aswitching element of a pixel in a display device having a large displayarea.

Furthermore, when the display devices with large display areas aremanufactured, there is a significant problem of signal delay due toresistance of a signal line. For this reason, a material with a lowelectric resistance value is used for a material of the signal line. Inaddition, a structure in which an auxiliary electrode is provided in apixel portion is disclosed in Patent Document 3.

REFERENCE

-   [Patent Document 1] Japanese Published Patent Application No.    2007-123861-   [Patent Document 2] Japanese Published Patent Application No.    2007-096055-   [Patent Document 3] Japanese Published Patent Application No.    2003-288994

SUMMARY OF THE INVENTION

Further, an increase not only in an area but also in definition ofdisplays in the display devices has been demanded. For example, ultrahigh-definition display devices with a large number of pixels, such as afull high definition (MD) display, a 4k2k display, and an 8k4k display,have been developed. As the size and definition of display devices areincreased, the number of signal lines for inputting signals to pixels isincreased with an increase in the number of pixels.

EL display devices are broadly divided into top emission display devicesand bottom emission display devices. The top emission display devicesare suitable to increase definition because of having a higher apertureratio than the bottom emission display devices. A top emission ELdisplay device has a structure in which a layer containing an organiccompound is formed over a first electrode electrically connected to atransistor formed over a substrate, a second electrode having alight-transmitting property is provided over the layer containing anorganic compound, and light emitted passes through the second electrode.

As a material for the second electrode having a light-transmittingproperty, a material called a conductive film having alight-transmitting property (typically, indium tin oxide (ITO), indiumzinc oxide, or the like) is used. However, with the use of the material,film resistance is easily increased and a nonuniform potentialdistribution occurs due to a voltage drop, which might causemalfunctions such as a variation in luminance of a light-emittingelement.

In view of the above, a structure of an EL display device which has anincreased display area is provided. Further, a structure of an ELdisplay device which has a high definition display.

Thus, an auxiliary electrode is provided in contact with the conductivefilm having a light-transmitting property to enable an increase in adisplay area. Further, color filters overlap with a plurality of whitelight-emitting elements arranged in a pixel portion to enable a highdefinition display.

As the color filters, a red coloring layer is provided to face a redlight-emitting region (R), a green coloring layer is provided to face agreen light-emitting region (G), and a blue coloring layer is providedto face a blue light-emitting region (B). The white light-emittingelement overlaps with the red coloring layer in the red light-emittingregion (R), light emitted from the white light-emitting element isextracted through the red coloring layer, and thus red light isprovided. A black portion of the color filters, i.e., a light-shieldingfilm (also referred to as black matrix), blocks light in regions otherthan the light-emitting regions. Note that the light-shielding film isformed of a metal film (e.g., chromium) or an organic film containing ablack pigment.

Note that the auxiliary electrode is formed over a first partitionprovided between the adjacent first electrodes. The angle between a sidesurface of the first partition and a top surface of the substrate, i.e.,a taper angle, is less than 90°. A second partition is provided incontact with a top surface and side surfaces of the auxiliary electrode,and the layer containing an organic compound is divided owing to a stepheight between the first partition and the second partition.

The second partition is formed over the first partition together withthe auxiliary electrode and covers at least the side surfaces of theauxiliary electrode, and the layer containing an organic compound is notformed on side surfaces of the second partition when the secondpartition is seen in a cross section. For example, the angle between theside surface of the second partition and the top surface of thesubstrate is more than or equal to 90° and less than or equal to 135°.

The second partition has the side surfaces on which the layer containingan organic compound is not formed when seen in the cross section,whereby a first layer containing an organic compound is formed on thefirst partition so that an edge thereof is in contact with the firstpartition, a second layer containing an organic compound is formed onand in contact with the second partition, and top edges of the secondpartition are substantially aligned with edges of the second layercontaining an organic compound; thus, the edge of the first layercontaining an organic compound is divided from the edge of the secondlayer containing an organic compound.

The first partition is formed of an insulating material and formed tocover the periphery of an edge of the first electrode, and a regionwhere the first electrode is not covered with the first partition servesas the light-emitting region.

For the auxiliary electrode, a film or a laminated film including anelement selected from Ag, Cu, Mg, and Mo, an alloy material containingsuch an element as its main component, or a compound material containingsuch an element as its main component is formed by sputtering,evaporation, or the like. In the case of forming the auxiliary electrodeby evaporation, an evaporation mask is used so that the auxiliaryelectrode has a top surface with a desired shape. In the case of formingthe auxiliary electrode by sputtering, photolithography is used to forma resist mask and etching is performed so that the auxiliary electrodehas a top surface with a desired shape.

A display device of the present invention disclosed in thisspecification includes a transistor over a substrate having aninsulating surface; a first electrode electrically connected to thetransistor; a first partition covering the periphery of an edge of thefirst electrode; a layer containing an organic compound over the firstelectrode; a second electrode having a light-transmitting property overthe layer containing an organic compound; a third electrode that is anauxiliary electrode over the first partition; and a second partitioncovering side surfaces of the third electrode over the first partition.The second partition has an opening reaching the third electrode and thethird electrode is electrically connected to the second electrodethrough the opening.

In the above structure, the second electrode is formed over the firstpartition and between an edge of the layer containing an organiccompound and the second partition, so that the second electrode is incontact with the first partition.

As the second electrode having a light-transmitting property, a MgAgfilm having a thickness less than or equal to 20 nm, preferably morethan or equal to 15 nm and less than or equal to 20 nm is used. As longas the second electrode has a thickness less than or equal to 20 nm, thesecond electrode has a property of transmitting light emitted from thelayer containing an organic compound. Further, the MgAg film over whichindium tin oxide (ITO), indium zinc oxide, or the like is stacked may beused as the second electrode.

In the above structure, the auxiliary electrode preferably has athickness at least larger than that of the second electrode. Inaddition, in the above structure, the same material can be used for theauxiliary electrode and the second electrode. For example, it ispreferable that a MgAg film having a large thickness be used as theauxiliary electrode and a MgAg film having a small thickness be used asthe second electrode, in which case contact resistance can be reducedbecause the same material is used.

In the above structure, a coloring layer is further provided over thefirst electrode to enable a full-color display. In the above structure,it is preferable that a light-shielding film functioning as a blackmatrix be further provided over the second partition. The coloring layerand the black matrix are provided over a substrate which is differentfrom the substrate provided with the transistor and which is used forsealing the light-emitting element. Since the display device with theabove structure is a top emission display device, a substrate having aproperty of transmitting light from the light-emitting element is usedas the substrate provided with the coloring layer and the black matrix.

In the above structure, an oxide semiconductor material is used for asemiconductor layer of the transistor. The field-effect mobility of atransistor using the oxide semiconductor material is ten or more timesas large as that of a transistor using amorphous silicon. Therefore, thetransistor using the oxide semiconductor material can provide aperformance high enough to allow the use of the transistor as a pixelswitching element even in a large-sized display device. The field effectmobility of the transistor using amorphous silicon is approximately 0.5cm²/Vs in general, whereas the field effect mobility of the transistorusing the oxide semiconductor material is 10 cm²/Vs to 20 cm²/Vs orhigher than or equal to 20 cm²/Vs. Further, an active layer using anoxide semiconductor material can be formed by sputtering or the like;thus, the transistor using the oxide semiconductor material can beeasily manufactured without using a laser device, which is used inmanufacture of a transistor using polycrystalline silicon. Furthermore,the transistor using the oxide semiconductor material can bemanufactured on an existing production line of transistors usingamorphous silicon by just changing part of the line; thus, additionalspending on equipment can be minimized to reduce the manufacturing costof the transistor.

An oxide semiconductor containing at least In is used for the oxidesemiconductor material. Examples of the oxide semiconductor materialinclude indium oxide; two-component metal oxides such as an In—Zn-basedoxide, an In—Mg-based oxide, and an In—Ga-based oxide; three-componentmetal oxides such as an In—Ga—Zn-based oxide (also referred to as IGZO),an In—Al—Zn-based oxide, an In—Sn—Zn-based oxide, an In—Hf—Zn-basedoxide, an In—La—Zn-based oxide, an In—Ce—Zn-based oxide, anIn—Pr—Zn-based oxide, an In—Nd—Zn-based oxide, an In—Sm—Zn-based oxide,an In—Eu—Zn-based oxide, an In—Gd—Zn-based oxide, an In—Tb—Zn-basedoxide, an In—Dy—Zn-based oxide, an In—Ho—Zn-based oxide, anIn—Er—Zn-based oxide, an In—Tm—Zn-based oxide, an In—Yb—Zn-based oxide,and an In—Lu—Zn-based oxide; four-component metal oxides such as anIn—Sn—Ga—Zn-based oxide, an In—Hf—Ga—Zn-based oxide, anIn—Al—Ga—Zn-based oxide, an In—Sn—Al—Zn-based oxide, anIn—Sn—Hf—Zn-based oxide, and an In—Hf—Al—Zn-based oxide; and the like.

Note that here, for example, an In—Ga—Zn-based oxide means an oxidecontaining In, Ga, and Zn, and there is no limitation on the compositionratio of In, Ga, and Zn. Further, the In—Ga—Zn-based oxide may contain ametal element other than In, Ga, and Zn.

Further, in the above structure, a single crystal film, apolycrystalline film, a microcrystalline film, or a c-axis alignedcrystalline oxide semiconductor (CAAC-OS) film is used for thesemiconductor layer of the transistor.

The CAAC-OS film is not completely single crystal nor completelyamorphous. The CAAC-OS film is an oxide semiconductor film including acrystal component. Note that in most cases, the crystal component fitsinside a cube whose one side is less than 100 nm. In an image obtainedwith a transmission electron microscope (TEM), a grain boundary in theCAAC-OS film is not clearly found. Therefore, in the CAAC-OS film, areduction in electron mobility, due to the grain boundary, issuppressed.

In the crystal component included in the CAAC-OS film, a c-axis isaligned in a direction parallel to a normal vector of a surface wherethe CAAC-OS film is formed or a normal vector of a surface of theCAAC-OS film, triangular or hexagonal atomic arrangement which is seenfrom the direction perpendicular to the a-b plane is formed, and metalatoms are arranged in a layered manner or metal atoms and oxygen atomsare arranged in a layered manner when seen from the directionperpendicular to the c-axis. Note that, among crystal components, thedirections of the a-axis and the b-axis of one crystal component may bedifferent from those of another crystal component. In other words,because the a-axis and the b-axis vary among the crystal components inthe CAAC-OS film although the c-axes are aligned, the CAAC-OS film isnot an epitaxially grown film. In this specification, a simple term“perpendicular” includes a range from 85° to 95°. In addition, a simpleterm “parallel” includes a range from −5° to 5°.

The oxide semiconductor film can be formed to have a thickness more thanor equal to 1 nm and less than or equal to 30 nm (preferably more thanor equal to 5 nm and less than or equal to 10 nm) by sputtering,molecular beam epitaxy (MBE), CVD, pulsed laser deposition, atomic layerdeposition (ALD), or the like as appropriate. In addition, the oxidesemiconductor film may be formed with the use of a sputtering apparatusin which deposition is performed in a state where surfaces of aplurality of substrates are set substantially perpendicularly to asurface of a sputtering target.

The single crystal film, the polycrystalline film, the microcrystallinefilm, or the CAAC-OS film can be obtained by changing in depositionconditions of a deposition method, increasing the substrate temperatureat the time of deposition, or performing heat treatment after thedeposition as appropriate.

Furthermore, in the above structure, a fourth electrode formed of thesame material as the first electrode of the light-emitting element isfurther included. The fourth electrode is electrically connected to aterminal electrode. The auxiliary electrode is provided on and incontact with the fourth electrode. The second electrode of thelight-emitting element is provided on and in contact with the fourthelectrode. That is to say, in the display device, the auxiliaryelectrode is connected to a wiring in a lower layer at a portiondifferent from a portion where the auxiliary electrode is connected to awiring in an upper layer. Specifically, in the pixel portion, to improvean aperture ratio, the auxiliary electrode is preferably in contact withthe second electrode formed thereover to be electrically connected tothe second electrode; in a region outside the pixel portion, to enablean electrical connection in a large area so that electrical conductionis ensured, the fourth electrode is preferably provided with the use ofthe same mask as the first electrode.

An oxide semiconductor material is used for a semiconductor layer of atransistor and an auxiliary electrode is provided between adjacentlight-emitting elements to enable a large-area display. Further, in atop-emission EL display device, even the distance between the adjacentlight-emitting elements is shortened, the auxiliary electrode can beprovided between the adjacent light-emitting elements, which alsoenables a high definition display.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are cross-sectional views of one embodiment of thepresent invention.

FIGS. 2A and 2B are top views of one embodiment of the presentinvention.

FIGS. 3A and 3B are a cross-sectional view of one embodiment of thepresent invention and a top view of a terminal portion.

FIGS. 4A and 4B illustrate electronic appliances.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention are described below in detail withreference to the accompanying drawings. However, the present inventionis not limited to the description below, and it is easily understood bythose skilled in the art that modes and details disclosed herein can bemodified in various ways without departing from the spirit and the scopeof the present invention. Further, the present invention is notconstrued as being limited to description of the embodiments.

Embodiment 1

In this embodiment, a structure of a display device which is oneembodiment of the present invention is described with reference to FIGS.1A and 1B, FIGS. 2A and 2B, and FIGS. 3A and 3B.

FIG. 2B is a general schematic view of the display device. The displaydevice in FIG. 2B includes a pixel portion 1502 including a plurality oflight-emitting elements over a substrate 1501 having an insulatingsurface. A sealing substrate 1503 including a color filter and thesubstrate 1501 are fixed so that the color filter overlaps with thepixel portion 1502. Terminals connected to the outside of the displaydevice are connected to FPCs 1505, 1506, 1507, 1508, 1509, 1510, 1511,and 1512. Note that the sealing substrate 1503 does not overlap with theterminals connected to the FPCs. FIG. 2B illustrates an example ofproviding an auxiliary electrode 151 with a net-like shape. Thepotential of the auxiliary electrode 151 is set to a fixed potential ora ground potential through the FPCs.

Although FIG. 2B illustrates an example where the auxiliary electrode isformed to surround a plurality of pixels, i.e., the plurality oflight-emitting elements, the auxiliary electrode 151 may be provided tosurround each of the light-emitting elements as illustrated in FIG. 2A.

FIG. 2A is a top view of a first substrate 100 seen from the side of asecond electrode 122, which illustrates part of the pixel of the displaydevice. FIG. 1A is a cross-sectional view taken along the dashed lineA1-A2 in FIG. 2A. FIG. 1B corresponds to a cross-sectional view takenalong the dashed line B1-B2 in FIG. 2A.

In the top view of FIG. 2A, some components (e.g., first partitions 124and second partitions 126) of the display device are omitted forsimplicity. The auxiliary electrode 151 is formed over the firstpartitions 124 and is not electrically connected to source wirings 156and gate wirings 154. Note that the angle between a side surface of thefirst partition 124 and a top surface of the substrate 100, i.e., thetaper angle, is less than 90°. It is preferable that the first partition124 have a forward tapered shape so that a film formed over the firstpartition 124 is prevented from being cut.

In the display device illustrated in FIG. 2A, the source wirings 156 areprovided parallel to (extending in the vertical direction in thedrawing) and apart from each other, and the gate wirings 154 areprovided parallel to (extending in the horizontal direction in thedrawing) and apart from each other. A substantially rectangular regionis surrounded by the source wirings 156 and the gate wirings 154. Thisregion serves as one pixel of the display device, and a plurality ofpixels is arranged in matrix. In addition, the auxiliary electrode 151is provided to surround the substantially rectangular region.

Further, a transistor 150 which controls driving of a light-emittingelement 130 and a transistor 152 which selects an intended pixel areformed in each pixel. Note that the display device is a top-emissiondisplay device in which a plurality of transistors can be arrangedwithout reducing the area of a light-emitting region; therefore, thenumber of transistors arranged in one pixel is not limited, and two ormore transistors, e.g., five transistors may be arranged. In addition,the second partition 126 is provided between the adjacent pixels. Thesecond partition 126 may be provided between every pair of adjacentpixels or provided at regular intervals.

Note that the angle between a side surface of the second partition 126and the top surface of the substrate 100 is more than or equal to 90°and less than or equal to 135°.

Although a top surface and side surfaces of the auxiliary electrode 151are covered with the second partition 126 and the auxiliary electrode151 is not in contact with the second electrode 122 in FIG. 1A, theauxiliary electrode 151 and the second electrode 122 are electricallyconnected to each other through an opening which is formed in the secondpartition 126 and reaches the auxiliary electrode 151 as illustrated inFIG. 1B, and the auxiliary electrode 151 and the second electrode 122have the same potential.

FIG. 1B illustrates a portion where the auxiliary electrode 151 and thesecond electrode 122 are connected to each other. In a region where alayer 119 containing an organic compound and formed on and in contactwith the auxiliary electrode 151 is not provided in the opening formedin the second partition 126, the second electrode 122 is provided on andin contact with the auxiliary electrode 151. In addition, a layer 121containing an organic compound is provided over the second partition126. The layer 119 containing an organic compound over the auxiliaryelectrode 151 is divided from the layer 121 containing an organiccompound over the second partition 126 by the second partition 126 andis also divided from a layer 120 containing an organic compound over afirst electrode 118 by the second partition 126. Note that the secondpartition 126 divides the layer 121 containing an organic compound overthe second partition 126 and the layer 120 containing an organiccompound over the first electrode 118 from each other.

The layer 119 containing an organic compound over the auxiliaryelectrode 151, the layer 120 containing an organic compound over thefirst electrode 118, and the layer 121 containing an organic compoundover the second partition 126 are formed at the same time and aredivided from each other with the second partition 126.

In addition, the second electrode 122 is also formed in contact with theside surfaces of the second partition 126 and the top surface of thefirst partition. In the case where the angle between the side surface ofthe second partition 126 and the top surface of the substrate 100 ismore than 135° or in the case where the second partition 126 has a largethickness, the second electrode 122 might not be formed on the sidesurfaces of the second partition 126.

The display device illustrated in FIG. 1A includes a first buffer layer104 provided over the first substrate 100, the transistor 150 whichcontrols the driving of the light-emitting element and is provided overthe first buffer layer 104, the light-emitting element 130 electricallyconnected to the transistor 150, the first partitions 124 surrounding alight-emitting region of the light-emitting element 130, the auxiliaryelectrode 151 formed over the first partitions 124, and the secondpartitions 126 formed over the auxiliary electrode 151 and the firstpartitions 124. In the display device illustrated in FIG. 1A, a secondsubstrate 160 is provided with light-shielding films 164 and coloringlayers 166, and the second substrate 160 and the first substrate 100 arebonded to each other with a first adhesive layer 170 and a secondadhesive layer. Although not illustrated, the second adhesive layer hasa closed-loop shape surrounding the pixel portion and is in contact withside surfaces of the first adhesive layer when seen from the above.

The transistor 150 includes a gate electrode 106 formed over the firstbuffer layer 104, a gate insulating layer 108 formed over the gateelectrode 106, a semiconductor layer 110 formed over the gate insulatinglayer 108, and a source electrode 112 a and a drain electrode 112 bformed over the semiconductor layer 110. The transistor 150 is coveredwith a first insulating layer 114, a second insulating layer 116, and athird insulating layer 117. In the transistor 150, a connectionelectrode 115 electrically connected to the drain electrode 112 bthrough an opening formed in the first insulating layer 114 and thesecond insulating layer 116 is formed; the connection electrode 115 iselectrically connected to the first electrode 118 over the thirdinsulating layer 117 through an opening formed in the third insulatinglayer 117. The first electrode 118, the layer 120 containing an organiccompound and formed over the first electrode 118, and the secondelectrode 122 and formed over the layer 120 containing an organiccompound are provided over the third insulating layer 117.

Further, the display device illustrated in FIG. 1A is a top-emissiondisplay device in which light from the light-emitting element 130 isemitted from the second substrate 160 side through the coloring layer166. Therefore, a substrate having a light-transmitting property, suchas a glass substrate or a plastic substrate, is used as the secondsubstrate 160.

Although not illustrated in FIG. 1A, the transistor 152 illustrated inFIG. 2A has the same structure as the transistor 150. However, the size(e.g., channel length and channel width) of each transistor and aconnection and the like of the transistors can be adjusted asappropriate by practitioners.

Here, an example of a method for manufacturing the transistor isdescribed below.

First, the first buffer layer 104 is formed over the first substrate. Asingle layer or stacked layers of silicon nitride, silicon oxynitride,silicon nitride oxide, or the like is preferably formed as the firstbuffer layer 104. The first buffer layer 104 is not necessarily providedif it is not needed.

Next, a conductive film is formed over the first buffer layer 104, and aphotolithography process and an etching step are performed thereon, sothat the gate electrode 106 is formed.

The gate electrode 106 can be formed using a single layer or stackedlayers of a metal material such as molybdenum, titanium, chromium,tantalum, tungsten, aluminum, copper, neodymium, or scandium, or analloy material which contains any of these elements.

Next, the gate insulating layer 108 is formed over the gate electrode106. As the gate insulating layer 108, a single layer or stacked layersof silicon oxide, silicon nitride, silicon oxynitride, silicon nitrideoxide, or aluminum oxide can be formed by plasma CVD, sputtering, or thelike.

Next, a semiconductor layer is formed, and a photolithography processand an etching step are performed thereon, so that the semiconductorlayer 110 with an island shape is formed.

An oxide semiconductor material is used to form a material of thesemiconductor layer 110. As the oxide semiconductor material, anIn—Ga—Zn—O-based metal oxide or the like can be used as appropriate.Note that as the semiconductor layer 110, an oxide semiconductormaterial which is an In—Ga—Zn—O-based metal oxide is preferably used, inwhich case the semiconductor layer 110 has low off-state current toallow a reduction in an off-state leakage current of the light-emittingelement formed later.

Next, a conductive film is formed over the gate insulating layer 108 andthe semiconductor layer 110, and a photolithography process and anetching step are performed thereon, whereby the source electrode 112 aand the drain electrode 112 b are formed.

As the conductive film used for the source electrode 112 a and the drainelectrode 112 b, for example, a metal film containing an elementselected from Al, Cr, Cu, Ta, Ti, Mo, and W, a metal nitride filmcontaining any of these elements (a titanium nitride film, a molybdenumnitride film, or a tungsten nitride film), or the like can be used.

Next, the first insulating layer 114 is formed over the semiconductorlayer 110, the source electrode 112 a, and the drain electrode 112 b. Asthe first insulating layer 114, an inorganic insulating film such as asilicon oxide film, a silicon oxynitride film, or an aluminum oxide filmcan be used.

Next, the second insulating layer 116 is formed over the firstinsulating layer 114.

As the second insulating layer 116, an insulating film with aplanarization function is preferably selected to reduce surfaceunevenness due to the transistor. For example, an organic material suchas a polyimide resin, an acrylic resin, or a benzocyclobutene resin canbe used. Other than such organic materials, it is also possible to use alow-dielectric constant material (a low-k material) or the like.

Next, the opening reaching the drain electrode 112 b is formed in thefirst insulating layer 114 and the second insulating layer 116 by aphotolithography process and an etching step. As a method for formingthe opening, dry etching, wet etching, or the like may be selected asappropriate.

Then, a conductive film is formed over the second insulating layer 116and the drain electrode 112 b, and a photolithography process and anetching step are performed thereon, whereby the connection electrode 115is formed. Through the above-described steps, the transistor 150 can bemanufactured. The transistor 150 is an n-channel transistor.

An example of a method for forming the light-emitting element 130connected to the transistor 150 is described below.

The third insulating layer 117 is formed over the second insulatinglayer 116. For the third insulating layer 117, a material which is thesame as that of the second insulating layer 116 can be used, and aninsulating film with a planarization function is preferably selected toreduce surface unevenness due to the transistor.

Next, the opening reaching the connection electrode 115 is formed in thethird insulating layer 117 by a photolithography process and an etchingstep.

Then, a conductive film is formed over the third insulating layer 117and the connection electrode 115, and a photolithography process and anetching step are performed thereon, whereby the first electrode 118 isformed.

For the first electrode 118, a material which efficiently reflects lightemitted from the layer 120 containing an organic compound (which isformed later) and functioning as a light-emitting layer is preferablyused, in which case the light-extraction efficiency can be improved.Note that the first electrode 118 may have a stacked-layer structure.For example, a conductive film of metal oxide, a titanium film, or thelike is formed to have a small thickness on a side in contact with thelayer 120 containing an organic compound, and a metal film (aluminum, analloy containing aluminum, silver, or the like) having high reflectancecan be used on the other side. With such a structure, formation of aninsulating film between the layer 120 containing an organic compound andthe metal film (aluminum, an alloy containing aluminum, silver, or thelike) having high reflectance can be suppressed, which is preferable. Inthis embodiment, the first electrode 118 has a three-layer structure inwhich a 50-nm-thick titanium film, a 200-nm-thick aluminum film, and an8-nm-thick titanium film are stacked in this order.

Next, the first partition 124 is formed over the first electrode 118.

An organic insulating material or an inorganic insulating material isused to form the first partition 124. It is particularly preferable thatthe first partition 124 be formed using a photosensitive resin materialand be formed to have a sidewall having an inclined surface withcontinuous curvature.

Next, a conductive film is formed over the first partition 124, and aphotolithography process and an etching step are performed thereon, sothat the auxiliary electrode 151 is formed. For the auxiliary electrode151, a film or a laminated film including an element selected from Ag,Cu, Mg, and Mo, an alloy material containing such an element as its maincomponent, or a compound material containing such an element as its maincomponent is formed by sputtering, evaporation, or the like. In the caseof performing a photolithography process and an etching step, etchingconditions and a material are selected so that the first electrode 118remains. In this embodiment, evaporation is performed with the use of anevaporation mask to selectively form a MgAg film over the firstpartition 124, whereby the auxiliary electrode 151 is formed.

Next, the second partition 126 is formed over the first partition 124.Note that the second partition 126 has a thickness larger than that ofthe auxiliary electrode 151.

The shape of the second partition 126 is important because the secondpartition 126 needs to divide a layer containing an organic compound andformed later. The second partition 126 has a cross-sectional shape withwhich the angle between the side surface of the second partition 126 andthe top surface of the first substrate 100 is more than or equal to 90°and less than or equal to 135°. For example, the second partition 126described in this embodiment has a reverse tapered shape. Here, thereverse tapered shape refers to a shape whose side portion or topportion extends outside the bottom portion in a direction parallel tothe substrate.

An inorganic insulating material or an organic insulating material canbe used to form the second partition 126. As the organic insulatingmaterial, for example, a negative or positive type photosensitive resinmaterial, a non-photosensitive resin material, or the like can be used.

The opening reaching the auxiliary electrode 151 is formed when thesecond partition 126 is formed or after the second partition 126 isformed. This opening is necessary to electrically connect the auxiliaryelectrode 151 and the second electrode formed later. In this embodiment,the negative type photosensitive resin material is used. Having higherdefinition than the positive type photosensitive resin material, thenegative type photosensitive resin material allows the opening reachingthe auxiliary electrode 151 to be formed finely when used as the secondpartition 126, which also makes it possible to reduce the size of theopening. Therefore, in the case of a high definition display device,even when the distance between the pixels is short, the second partition126 can be formed and the opening reaching the auxiliary electrode 151can be formed finely.

Next, the layer containing an organic compound is formed over the firstelectrode 118, the first partition 124, and the second partition 126.The layer containing an organic compound can be formed by evaporation(including vacuum evaporation) or the like.

The layer containing an organic compound is formed to be divided by thesecond partition 126. The layer 119 containing an organic compound overthe auxiliary electrode 151, the layer 120 containing an organiccompound over the first electrode 118, and the layer 121 containing anorganic compound over the second partition 126 are divided from eachother by the second partition 126. Only the layer 120 containing anorganic compound and formed over the first electrode 118 functions asthe light-emitting layer of the light-emitting element 130.

The layer 120 containing an organic compound and formed over the firstelectrode 118 may have a single-layer or a stacked-layer structure.Light emitted from the layer 120 containing an organic compound ispreferably white, and light having a peak in each of red, green, andblue wavelength regions is preferable.

Next, the second electrode 122 is formed over the layers containing anorganic compound. The second electrode 122 is not divided by the secondpartition 126 and is electrically connected to the auxiliary electrode151.

As the second electrode 122, a metal film having a thickness less thanor equal to 20 nm, preferably more than or equal to 15 nm and less thanor equal to 20 nm is used. Typically, a MgAg film is used. Further, theMgAg film over which indium tin oxide (ITO), indium zinc oxide, or thelike is stacked may be used as the second electrode.

Alternatively, as the second electrode 122, a conductive material filmwhich has a light-transmitting property and includes at least a layer ofgraphene may be used; for example, a stack in which a layer of ironchloride (FeCl₃) is sandwiched between a plurality of layers ofgraphene, such as five layers of graphene each pair of which sandwichesa layer of iron chloride, can be used. The stack of the layers ofgraphene and the layer of iron chloride is a light-transmittingconductive film and has a light transmittance of higher than 80%.

Note that one of the first electrode 118 and the second electrode 122functions as an anode of the light-emitting element, and the otherfunctions as a cathode of the light-emitting element. It is preferableto use a substance having a high work function for the electrode whichfunctions as an anode, and a substance having a low work function forthe electrode which functions as a cathode.

Through the above steps, it is possible to form the light-emittingelement 130 and the transistor 150, which controls driving of thelight-emitting element, over the same substrate.

In addition, a method for forming the second substrate 160 provided withthe light-shielding films 164, the coloring layers 166 functioning ascolor filters, and an overcoat 168 is described below.

A second buffer layer 162 is formed over the second substrate 160. Thesecond buffer layer 162 can be formed using a material and a methodsimilar to those of the first buffer layer 104.

Next, a material film is fondled over the second buffer layer 162, and aphotolithography process and an etching step are performed thereon,whereby the light-shielding films 164 functioning as black matrixes areformed. For the light-shielding films 164, a low reflectance metal filmsuch as a titanium film or a chromium film, or an organic resin filmimpregnated with black pigment or black dye can be used.

Next, the coloring layers 166 of several colors functioning as colorfilters are formed over the second buffer layer 162 and thelight-shielding films 164. The coloring layers 166 are colored layerstransmitting light in specific wavelength regions. For example, a red(R) coloring layer transmitting light of a red wavelength region, agreen (G) coloring layer transmitting light of a green wavelengthregion, a blue (B) coloring layer transmitting light of a bluewavelength region, and the like can be used. Each coloring layer isformed in a desired position with a known material by printing, inkjet,etching using photolithography, or the like.

Although a method of using three colors of R, G, and B is describedhere, the present invention is not limited to this structure. Astructure in which four colors of R, G, B, and Y (yellow) are used or astructure in which five or more colors are used may be employed.

Next, the overcoat 168 is formed over the light-shielding films 164 andthe coloring layers 166.

An organic resin film formed of acrylic, polyimide, or the like can beused to form the overcoat 168. The overcoat 168 can prevent diffusion ofan impurity component and the like contained in the coloring layers 166to the light-emitting element side. The overcoat 168 may have astacked-layer structure of an organic resin film and an inorganicinsulating film. Silicon nitride, silicon oxide, or the like can be usedfor the inorganic insulating film. Note that the overcoat 168 is notnecessarily provided.

Through the above steps, the second substrate 160 provided with thesecond buffer layer 162, the light-shielding films 164, the coloringlayers 166, and the overcoat 168 is formed.

Next, the first substrate 100 and the second substrate 160 are alignedand bonded to each other using the first adhesive layer 170.

There is no particular limitation on the first adhesive layer 170, and alight-transmitting adhesive having high refractive index and capable ofbonding the second electrode 122 provided over the first substrate 100and the overcoat 168 provided over the second substrate 160 can be used.A substance having molecular size less than or equal to the wavelengthof light and functioning as a dry agent (zeolite or the like), or afiller with a high refractive index (titanium oxide, zirconium, or thelike) is preferably mixed to the adhesive because reliability orlight-extraction efficiency of the light-emitting element 130 isimproved.

Further, a sealing film with low moisture permeability may be formedbetween the first adhesive layer 170 and the second electrode 122. Asthe sealing film with low moisture permeability, for example, siliconoxide, silicon nitride, aluminum oxide, or the like can be used.

Through the above steps, an active matrix display device can bemanufactured.

In the case of a display device including 2000 scan lines (considering4k2k images with 4096×2160 pixels, 3840×2160 pixels, or the like), arow-selection period is 1240000 second (≈4.2 μs) if signal delay or thelike caused by a wiring is not taken into consideration.

Since the oxide semiconductor material is used for the semiconductorlayer of the transistor and the auxiliary electrode 151 is formed, ahigh definition display device including 2000 or more scan lines can beprovided.

When the auxiliary electrode 151 is provided, there are portions wherethe auxiliary electrode 151 intersects with the gate electrode and thesource electrode. Further, when a display area is increased, electricalconnection between the auxiliary electrode 151 and an electrode in alower portion is preferably formed at a plurality of points to improveyield. The electrode in the lower portion can be formed in the same stepas the gate electrode, the source electrode, or the connectionelectrode. FIG. 3A illustrates examples of a cross-sectional structureand a connection between electrodes of a terminal portion 210 includinga terminal electrode 217 to which FPCs are attached.

As illustrated in FIG. 3A, on the periphery of the terminal portion, theauxiliary electrode 151 can be electrically connected to wirings 216 and218 for terminals which are formed in the same step as the firstelectrode 118. FIG. 3B is an enlarged top view of part of FIG. 2B,specifically a top view of the periphery of a portion where the FPCs1505 and 1512 are attached to the terminal electrode. In the pixelportion, as illustrated in FIG. 1B, the auxiliary electrode 151 is incontact with the second electrode 122 and thus is connected to thesecond electrode 122; on the other hand, in a region outside the pixelportion, as illustrated in FIG. 3B, the auxiliary electrode 151 iselectrically connected to the wiring 218 for a terminal which is formedin the same step as the first electrode 118 and thus is electricallyconnected to the second electrode 122 in contact with the wiring 218 fora terminal. In the pixel portion, to improve the aperture ratio, theauxiliary electrode 151 is in contact with the second electrode 122 andthus is connected to the second electrode 122, whereas in the regionoutside the pixel portion, to ensure electrical conduction, theauxiliary electrode 151 is connected so as to have a large contact area.

Further, as illustrated in FIG. 3B, the terminal electrode 217 is formedon an edge of the wiring 216 for a terminal and is electricallyconnected to the FPCs. The terminal electrode 217 is formed in such amanner that a conductive film of ITO or the like is formed by sputteringbefore the first partition 124 is formed and then, a photolithographyprocess and an etching step are performed thereon. The conductive filmof ITO or the like may be selectively formed over the first electrode118 in the pixel portion, so that optical path lengths are adjusted,which improves color purity and luminance; for example, the conductivefilm is formed in the red pixel and is not formed in the blue pixel, sothat they are different in an optical path length between the layercontaining an organic compound and the first electrode.

A second adhesive layer 219 fixes the second substrate 160 to the thirdinsulating layer 117 over the first substrate 100. The second adhesivelayer 219 is shown by the dashed line in FIG. 3B. The second adhesivelayer 219 has low adhesion to a metal material which composes thewirings and electrodes; therefore, as illustrated in FIG. 3B, thewirings 216 and 218 for terminals are electrically connected to eachother through an electrode 213 so that the wirings do not overlap withthe second adhesive layer 219 to be in contact with the second adhesivelayer 219. Further, regions where the auxiliary electrode 151 isconnected to the wiring 218 for a terminal are positioned to surround apixel portion 220. Note that although not illustrated in FIG. 3B, thesecond electrode 122 is formed over the second partition 126 coveringthe auxiliary electrode 151 and the periphery of an edge of the secondelectrode 122 is provided between the auxiliary electrode 151 and theterminal electrode 217 when seen from above.

In addition, the wirings 216 and 218 for terminals are connected to thesecond electrode 122. The wirings 216 and 218 for terminals can beconnected to electrodes 214 and 215 which are formed in the same step asthe connection electrode at a plurality of points. The electrode 215 canalso be connected to an electrode 211 formed in the same step as thegate electrode or an electrode 212 and the electrode 213 which areformed in the same step as the source electrode at a plurality ofpoints. Further, a protective circuit in which an oxide semiconductormaterial is used may be provided between the terminal portion 210 andthe pixel portion 220 if needed.

As described above, in the display device described in this embodiment,the oxide semiconductor material is used for the semiconductor layer ofthe transistor and the auxiliary electrode is provided between theadjacent light-emitting elements, which enables a large-area display.Further, in a top-emission EL display device, even the distance betweenthe adjacent light-emitting elements is shortened, the auxiliaryelectrode can be provided between the adjacent light-emitting elements,which enables a high definition display.

Embodiment 2

A display device disclosed in this specification can be applied to avariety of electronic appliances (including game machines). Examples ofthe electronic appliances include a television device (also referred toas a television or a television receiver), a monitor of a computer,cameras such as a digital camera and a digital video camera, a digitalphoto frame, a mobile phone, a portable game machine, a portableinformation terminal, an audio reproducing device, a game machine (e.g.,a pachinko machine or a slot machine), and a game machine console.Specific examples of the electronic appliances are illustrated in FIGS.4A and 4B.

FIG. 4A illustrates a table 9000 having a display portion. In the table9000, a display portion 9003 is incorporated in a housing 9001. Adisplay device manufactured with the use of one embodiment of thepresent invention can be used for the display portion 9003, and an imagecan be displayed on the display portion 9003. Note that the housing 9001is supported by four leg portions 9002. Further, a power cord 9005 forsupplying power is provided for the housing 9001.

The display portion 9003 has a touch-input function. When a user touchesdisplayed buttons 9004 displayed on the display portion 9003 of thetable 9000 with his/her fingers or the like, the user can carry outoperation of the screen and input of information. Further, when thetable may be made to communicate with home appliances or control thehome appliances, the display portion 9003 may function as a controldevice which controls the home appliances by operation on the screen.

Further, the screen of the display portion 9003 can be placedperpendicular to a floor with a hinge provided for the housing 9001;thus, the table 9000 can also be used as a television device. When atelevision device having a large screen is set in a small room, an openspace is reduced; however, when a display portion is incorporated in atable, a space in the room can be efficiently used.

FIG. 4B illustrates a television device 9100. In the television device9100, a display portion 9103 is incorporated in a housing 9101. Adisplay device manufactured with the use of one embodiment of thepresent invention can be used in the display portion 9103, and an imagecan be displayed on the display portion 9103. Note that the housing 9101is supported by a stand 9105 here.

The television device 9100 can be operated with an operation switch ofthe housing 9101 or a separate remote controller 9110. Channels andvolume can be controlled with an operation key 9109 of the remotecontroller 9110 so that an image displayed on the display portion 9103can be controlled. Furthermore, the remote controller 9110 may beprovided with a display portion 9107 for displaying data output from theremote controller 9110.

The television device 9100 illustrated in FIG. 4B is provided with areceiver, a modem, and the like. With the receiver, the televisiondevice 9100 can receive a general television broadcast. Further, whenthe television device 9100 is connected to a communication network bywired or wireless connection via the modem, one-way (from a transmitterto a receiver) or two-way (between a transmitter and a receiver orbetween receivers) data communication can be performed.

With the use of the display device described in the above embodiment inthe display portion 9103 of the television device, the television devicecan have a higher display quality than the conventional one.

This application is based on Japanese Patent Application serial No.2012-108940 filed with Japan Patent Office on May 10, 2012, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A light-emitting element comprising: a firstelectrode; a second electrode over the first electrode; a light-emittinglayer between the first electrode and the second electrode; a firstpartition covering an edge of the first electrode; a second partitionover the first partition; and a conductive layer between the firstpartition and the second partition, wherein the second partition coversat least a side surface of the conductive layer.
 2. The light-emittingelement according to claim 1, wherein a shape of the first partition isa forward tapered shape.
 3. The light-emitting element according toclaim 1, wherein an angle between a side surface of the first partitionand a bottom surface of the first partition is less than 90°.
 4. Thelight-emitting element according to claim 1, wherein a shape of thesecond partition is a reverse tapered shape.
 5. The light-emittingelement according to claim 1, wherein an angle between a side surface ofthe second partition and a bottom surface of the second partition ismore than or equal to 90° and less than or equal to 135°.
 6. Thelight-emitting element according to claim 1, wherein an edge of thelight-emitting layer is covered with the second electrode, and whereinthe second electrode is in contact with the first partition.
 7. Thelight-emitting element according to claim 1, further comprising acoloring layer over the second electrode.
 8. A light-emitting devicecomprising the light-emitting element according to claim
 1. 9. Alight-emitting element comprising: a first electrode; a second electrodeover the first electrode; a light-emitting layer between the firstelectrode and the second electrode; a first partition covering an edgeof the first electrode; a second partition over the first partition; anda conductive layer between the first partition and the second partition,wherein the second partition covers at least a side surface of theconductive layer, wherein the second partition has an opening reachingthe conductive layer, and wherein the conductive layer is electricallyconnected to the second electrode through the opening.
 10. Thelight-emitting element according to claim 9, wherein a shape of thefirst partition is a forward tapered shape.
 11. The light-emittingelement according to claim 9, wherein an angle between a side surface ofthe first partition and a bottom surface of the first partition is lessthan 90°.
 12. The light-emitting element according to claim 9, wherein ashape of the second partition is a reverse tapered shape.
 13. Thelight-emitting element according to claim 9, wherein an angle between aside surface of the second partition and a bottom surface of the secondpartition is more than or equal to 90° and less than or equal to 135°.14. The light-emitting element according to claim 9, wherein an edge ofthe light-emitting layer is covered with the second electrode, andwherein the second electrode is in contact with the first partition. 15.The light-emitting element according to claim 9, further comprising acoloring layer over the second electrode.
 16. A light-emitting devicecomprising the light-emitting element according to claim 9.